package com.coding.basic.queue;

import java.util.Stack;

/**
 * 用两个栈来实现一个队列
 *
 * @author liuxin
 */
public class QueueWithTwoStacks<E> {
    private Stack<E> stack1;
    private Stack<E> stack2;

    public QueueWithTwoStacks() {
        stack1 = new Stack<E>();
        stack2 = new Stack<E>();
    }

    public boolean isEmpty() {
        return stack1.isEmpty() && stack2.isEmpty();
    }

    public int size() {
        return stack1.size() + stack2.size();
    }

    public void enQueue(E item) {
        stack1.push(item);
    }

    public E deQueue() {
        if (isEmpty()) {
            throw new RuntimeException("Queue is empty");
        }
        moveStack1ToStack2();
        return stack2.pop();
    }

    private void moveStack1ToStack2() {
        while (!stack1.isEmpty()) {
            stack2.push(stack1.pop());
        }
    }
}

